package com.lagou.sqlSession;

import com.lagou.pojo.Configuration;
import com.lagou.pojo.MappedStatement;
import com.lagou.pojo.SqlType;

import java.lang.reflect.*;
import java.util.List;

public class DefaultSqlSession implements SqlSession {

    private Configuration configuration;

    public DefaultSqlSession(Configuration configuration) {
        this.configuration = configuration;
    }

    @Override
    public <E> List<E> selectList(String statementid, Object... params) throws Exception {

        //将要去完成对simpleExecutor里的query方法的调用
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementid);
        List<Object> list = simpleExecutor.query(configuration, mappedStatement, params);

        return (List<E>) list;
    }

    @Override
    public <T> T selectOne(String statementid, Object... params) throws Exception {
        List<Object> objects = selectList(statementid, params);
        if (objects.size() == 1) {
            return (T) objects.get(0);
        } else {
            throw new RuntimeException("查询结果为空或者返回结果过多");
        }
    }

    @Override
    public int insert(String statementId, Object... params) throws Exception {
        return update(statementId, params);
    }

    @Override
    public int delete(String statementId, Object... params) throws Exception {
        return update(statementId, params);
    }

    @Override
    public int update(String statementId, Object... params) throws Exception {
        SimpleExecutor simpleExecutor = new SimpleExecutor();
        MappedStatement mappedStatement = configuration.getMappedStatementMap().get(statementId);
        return simpleExecutor.update(configuration, mappedStatement, params);
    }

    @Override
    public <T> T getMapper(Class<?> mapperClass) {
        // 使用JDK动态代理来为Dao接口生成代理对象，并返回

        Object proxyInstance = Proxy.newProxyInstance(DefaultSqlSession.class.getClassLoader(), new Class[]{mapperClass}, new InvocationHandler() {
            @Override
            public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
                // 底层都还是去执行JDBC代码 //根据不同情况，来调用selctList或者selectOne
                // 准备参数 1：statmentid :sql语句的唯一标识：namespace.id= 接口全限定名.方法名
                // 方法名：findAll
                String methodName = method.getName();
                String className = method.getDeclaringClass().getName();

                String statementId = className + "." + methodName;

                SqlType sqlType = configuration.getMappedStatementMap().get(statementId).getSqlType();
                // 准备参数2：params:args
                // 获取被调用方法的返回值类型
                switch (sqlType) {
                    case INSERT: {
                        return rowCountResult(insert(statementId, args), method);
                    }
                    case UPDATE: {
                        return rowCountResult(update(statementId, args), method);
                    }
                    case DELETE: {
                        return rowCountResult(delete(statementId, args), method);
                    }
                    case SELECT:
                        return select(args, statementId, method.getGenericReturnType());
                    default:
                        throw new RuntimeException("Unknown execution method for: " + statementId);
                }
            }

            private Object select(Object[] args, String statementId, Type genericReturnType) throws Exception {
                // 判断是否进行了 泛型类型参数化
                if (genericReturnType instanceof ParameterizedType) {
                    List<Object> objects = selectList(statementId, args);
                    return objects;
                }

                return selectOne(statementId, args);
            }

            private Object rowCountResult(int rowCount, Method method) {
                final Object result;
                if (void.class.equals(method.getReturnType())) {
                    result = null;
                } else if (Integer.class.equals(method.getReturnType()) || Integer.TYPE.equals(method.getReturnType())) {
                    result = rowCount;
                } else if (Long.class.equals(method.getReturnType()) || Long.TYPE.equals(method.getReturnType())) {
                    result = (long) rowCount;
                } else if (Boolean.class.equals(method.getReturnType()) || Boolean.TYPE.equals(method.getReturnType())) {
                    result = rowCount > 0;
                } else {
                    throw new RuntimeException("Mapper  has an unsupported return type: " + method.getReturnType());
                }
                return result;
            }
        });

        return (T) proxyInstance;
    }
}
